LONDON - A runaway chimp was shot dead after breaking out of his enclosure at an English zoo, his keepers said.

Chimpanzees Jonnie and Coco broke out of their compound Friday at the Whipsnade Zoo in Bedfordshire, about 35 miles north of London. The Zoological Society of London, which runs the zoo, said Coco was recaptured, but Jonnie could not immediately be caught and had to be killed.

Jonnie was still in the zoo at the time he was shot, said Christine Drabwell, a press officer at the Whipsnade Zoo. Officials declined to say how long he'd been free, saying an investigation was pending.

"It's just standard procedure, if the animal cannot be quickly and safely recaptured it will be shot," ZSL spokeswoman Alice Henchley said.

When asked why the chimps weren't shot with a tranquilizer gun or in another non-lethal manner, a zoo spokeswoman said that under their procedures, they have to shoot to kill when they have an animal who might be of danger to the public.

"We can't be sure with a tranquilzer," said the spokeswoman for the zoo who spoke on condition of anonymity in keeping with the organization's policy. "It doesn't work quickly enough."

Jonnie, an adult male, was gunned down by the zoo's specially trained firearms squad, Henchley said. She added that Jonnie and Coco's keepers were still trying to figure out how the apes escaped.